1. Field of the Invention
The present invention relates to a device and a method of fabricating a color conversion table, and a medium for recording a program for forming a color conversion table. In the invention grey scale color representing data, in a post-conversion color representing space, is corresponded to lattice points in a pre-conversion color representing space for converting grey scale color representing data between different color representing spaces.
2. Description of the Prior Art
There has conventionally been known as a color conversion table of this kind a color print system for performing color printing of a color image in a computer.
Inside the computer, the color image is displayed in a grey scale by the three primary colors of red, green and blue (R, G, B) for respective pixels arranged vertically and horizontally. In a general color printing device, printing is performed using the three colors of cyan, magenta and yellow (C, M, Y), or the four colors of (C, M, Y, K) added with black but with no grey scale. Accordingly, in performing color printing, there is an operation of color conversion from the three primary colors of red, green and blue (R, G, B) to the three colors of cyan, magenta and yellow (C, M, Y), and also an operation of grey scale conversion from grey scale display to display having no grey scale. Incidentally, although color space per se is one space, display has to differ depending on the definition of coordinates and accordingly, in the following, the space is referred to as a color representing space in accordance with the definition of coordinates, for convenience of explanation.
The color conversion from (R, G, B) display to (C, M, Y) display is not unequivocally determined by a conversion equation. Normally, a correspondence relationship is established, mutually, in respect of color spaces each having coordinates of respective grey scales. For convenience, the correspondence relationship may also be referred to as a corresponding relationship. The conversion is successively performed through this correspondence relationship. When a pre conversion (R, G, B) display is provided with 256 grey scales for each color, a color conversion table having elements of substantially 16,700,000 (256xc3x97256xc3x97256) must therefore be prepared.
For the sake of the efficient use of storage resources, the correspondence relationship is not prepared for all the coordinate values but, rather, for lattice points at pertinent discontinuous intervals. A interpolation calculation is thus used along therewith. That is, when it is intended to establish the correspondence relationship of a (C, M, Y) color representing space in respect of color of certain known coordinates in a (R, G, B) color representing space (i.e., RGB coordinates), a correspondence relationship among the lattice points surrounding the known coordinates is used. The correspondence relationship of the RGB and CMY coordinates is established after performing of linear interpolation or the like. The lattice points in each color space and their correspondence is stored as a color conversion table.
Such a color conversion table is generally provided along with a printer driver. Just one printer driver per se, including a color conversion table, is typically provided with a given color printing device. Therefore, a number of lattice points, determined based on storage constraints, is specified also in respect of the color conversion table.
The above-described conventional color conversion table, however, is not necessarily optimal with respect to a given user""s environment. The color conversion table is formed by the provider the printer driver based on general storage constraints, but there may be a case where a table is too large or, sometimes a case where a larger size would be more suitable for the table, depending on the user""s environment.
Furthermore, print quality may differ depending on the size of the color conversion table and, therefore, a constant size for the color conversion table may not be sufficient.
Accordingly, it is an object of the present invention to provide a device and a method for fabricating a color conversion table, capable of forming a color conversion table optimized to a given environment, such as that of a user or the like. It is also an object of the invention to provide a computer readable medium recording such a program for forming such an optimal color conversion table.
According to an aspect of the present invention, there is provided a device for fabricating a color conversion table in which a color conversion table corresponding grey scale color representing data in a post conversion color representing space to lattice points is formed in order to convert the grey scale color representing data between the different color representing spaces, the device including a pre conversion color conversion table for storing a corresponding relationship of conversion at a small number of lattice points and interpolating means for increasing the lattice points of the pre conversion color conversion table by an interpolation calculation and forming a color conversion table used in the conversion.
According to the present invention constituted as described-above, there is originally existed the pre conversion color conversion table having a small number of the lattice points, which requires little storage resource. Further, the interpolating means forms the color conversion table by increasing the lattice points of the pre conversion color conversion table by interpolation calculation and utilizes the formed color conversion table in color conversion.
The number of the lattice points in the pre conversion color conversion table may be relatively small in comparison with those in the formed color conversion table and has not necessarily to be an extremely small numerical value. Particularly, in the case of three-dimensional lattice points, the amount of lattice points is changed in a cubic ratio. That is, when the number of points is halved, the size of the color conversion table is reduced to xe2x85x9 of the original and accordingly, enormous effect is achieved to storage resource only with a small difference therebetween.
Therefore, according to the present invention, the color conversion table is formed from the pre conversion color conversion table having a small size by increasing the lattice points and therefore, only minimum storage resource is needed when the color conversion is not performed whereas when the color conversion is performed, the color conversion table having a necessary magnitude can be formed and accordingly, the present invention can provide a further flexible device of fabricating a color conversion table. Naturally, the table may be spread when it is necessary and is not spread when it is not necessary or may be left in the spread state when there is allowance in storage resource.
In respect of the interpolation calculating means, various calculations are applicable. Hence, it is a further object of the present invention to provide a further specific constitution in respect of the interpolation calculating means.
According to a device of fabricating a color conversion table of the present invention, the interpolating means comprises nonlinear interpolation calculating means for performing an interpolation by a nonlinear interpolation calculation from a corresponding relationship of a plurality of lattice points.
According to the present invention constituted as described-above, the nonlinear interpolation calculating means of the interpolating means interpolates the lattice points by the nonlinear interpolation calculation from the corresponding relationship in the plurality of lattice points.
The corresponding relationship in the increased lattice points is accurately reproduced by performing the nonlinear interpolation calculation. Accordingly, a result having very excellent reproducing performance can be provided even with a small number of lattice points in the pre conversion color conversion table.
That is, according to the present invention, the lattice points are increased by the nonlinear interpolation calculation and therefore, the accuracy of increased lattice points is improved and an excellent color conversion result can be obtained. Conversely, this amounts to an effect where excellent result can be obtained even with a small number of lattice points.
Meanwhile, the interval of the lattice points in the pre conversion color conversion table relates to the interpolation calculation. Hence, it is a further object of the present invention to provide a further preferable interval between lattice points.
According to a device of fabricating a color conversion table of the present invention, the pre conversion color conversion table is constituted by lattice points at uniform intervals.
Although the interval between lattice points may not necessarily be uniform in the nonlinear interpolation calculation, coefficients of calculating equations become complicated with a non uniform lattice interval. Further, at least in the case where lattice points are increased by interpolation calculation in a three-dimensional cubic body, an operation of calculating intermediate lattice points from a plurality of lattice points for each axial direction, is needed, and when in that case, coefficients of calculating equations become complicated, the interpolation calculation becomes complicated and the operation is troublesome. By contrast, according to the present invention constituted as described above, a situation where loop processing is easy to apply since some coefficients or the like become constant in the case of the uniform lattice point interval, is caused.
Accordingly, in the present invention, the nonlinear interpolation calculation can be prevented from being complicated by setting the lattice points of the pre conversion color conversion table at equal intervals by which reduction in calculation time period can be achieved.
Naturally, there may be a case that the intervals may preferably be uniform depending on other interpolation calculation except the nonlinear interpolation calculation or a case where the intervals are preferably nonuniform and intervals may be pertinently changed in accordance with the interpolation calculation.
Also, it is a further object of the present invention to provide a constitution where calculation other than the nonlinear interpolation calculation is used.
According to a device of fabricating a color conversion table of the present invention, the interpolating means comprises linear interpolation calculating means for performing an interpolation by a linear interpolation calculation from a corresponding relationship of a plurality of lattice points.
In the case of the linear interpolation, there is a merit where calculation equations per se are not complicated and there is a property where lattice points necessary for calculation are two points in respect of the axial direction. Accordingly, an accurate corresponding relationship can easily be obtained by finely distributing lattice points at portions where the corresponding relationship is significantly changed. Conversely, coarse distribution of lattice points can easily be performed at portions where the corresponding relationship is not significantly changed.
That is, according to the present invention, the interpolation calculation can be performed simply by utilizing linear interpolation having a small amount of equation. Further, there is provided a merit capable of achieving promotion of accuracy even with the easiness in liner calculation by densely distributing lattice points at portions of a significant change in the corresponding relationship by utilizing the easiness of the linear interpolation.
The number of lattice points which the interpolation calculating means increases is not necessarily constant. Hence, it is a further object of the present invention to flexibly deal with the number of lattice points.
According to a device of fabricating a color conversion table in the present invention, in respect of the interpolating means, the number of lattice points to be increased by interpolation can be selected.
The size of the color conversion table is changed by the increased number of lattice points and depending on the interpolation calculation, the lattice points may effect influence on the conversion accuracy in color conversion. Therefore, since the number of lattice points increased by interpolation is selectable, an optimum number of the lattice points in respect of environment of a user can be constituted.
That is, according to the present invention, the number of lattice points to be increased can be selected and accordingly, a color conversion table further flexibly suitable for environment of a user can be formed, as in determining the size of the color conversion table in conformity with storage resource of a user. Thereby, a plurality of sizes of color conversion tables can be formed and accordingly, the tables can be utilized by suitably selecting them as necessary.
Also, it is further object of the present invention to further simplify setting of lattice points.
According to a device of fabricating a color conversion table of the present invention, the interpolating means sets the increased number of lattice points in accordance with environment.
The size of the color conversion table is changed and the hit rate of color conversion is changed in accordance with the number of lattice points. Further, interpolation calculation is facilitated depending on positions of the increased lattice points. Therefore, optimum color conversion can be achieved by increasing lattice points synthetically in accordance with environment. As a policy of selecting lattice points increased in accordance with environment, when storage resource is large, a color conversion table having a large size may be provided, when promotion of color conversion accuracy is desired in the case where the more the lattice points, the higher the color conversion accuracy, the lattice points maybe increased and when multiplication or division at a power of 2 is easy in the interpolation calculation, the interval between the lattice points may be set to a length in accordance with the power of 2.
That is, according to the present invention, the lattice points having a number in accordance with environment are selected and therefore, a user does not have to carry out troublesome setting operation.
Further, in order to select lattice points which are increased with a similar object, according to a device of fabricating a color conversion table of the present invention, the interpolating means sets the increased number of lattice points in accordance with the kind of converted image.
As described above, there is the case where the more the lattice points, the higher the color conversion accuracy and in that case, depending on image, high color conversion accuracy may be required or not so high color conversion accuracy may be required. Therefore, when information of converted image requires high color conversion accuracy, the lattice points are increased as many as possible and when a not so high color conversion accuracy is required, the lattice points are not increased so much. As a policy in this case, for example, when the kind of converted image can be known from an operating system or the like, it is effective that the lattice points are increased as many as possible by determining that importance of color information is high as in photograph or the like if the expander of file is a bit map whereas the lattice points are not increased so much by determining that the importance of color information is low in the case where the expander of file designates a draw data or a business graph.
Therefore, according to the present invention, the increase in lattice points is selected in accordance with converted image and therefore, a disadvantage of enlarging excessively and unnecessarily the color conversion table or enlarging the color conversion table only insufficiently can be dispensed with.
Also, it is a further object of the present invention to be able to perform color conversion at a higher speed and accurately.
According to other aspect of the present invention, there is provided a device of fabricating a color conversion table in which the color conversion table is referred to by a computer, the pre conversion color conversion table is stored normally to an auxiliary storage device of the computer and is spread in a main storage region of the computer when the reference of the color conversion table is executed.
When a computer refers the color conversion table, the operation is at a high speed if the table is spread in a so-called main storage region. Meanwhile, much capacity is needed to the color conversion table and accordingly, it is waste of resource to always spread the table in the main storage region. Therefore, the pre conversion color conversion table is normally stored to an auxiliary storage device of the computer and is spread to the main storage region of the computer in referring to the color conversion table.
Thereby, effective use of resource and high speed can be realized. In this case, the main storage region must be interpreted in a broad sense and it may be RAM in respect of CPU or a volatile RAM disc or the like. That is, a storage medium capable of accessing at a high speed and permitting only temporary use may be applied.
Naturally, specific examples of the thought of the present invention are not necessarily limited to the above-described but according to other example of the present invention, there is provided a method of fabricating a color conversion table for forming the color conversion table where lattice points in a pre conversion color representing space are corresponded by grey scale color representing data in a post conversion color representing space in order to convert the grey scale color representing data between the different color representing spaces, in which the lattice points are formed to increase by interpolation calculation.
Accordingly, the present invention is not necessarily limited to a substantial device but is effective as a method thereof.
By the way, there are cases where the color conversion device having such a color conversion table is present by itself or is utilized in a state where it is integrated to a certain instrument, and so on and accordingly, the thought of the present invention is not limited thereto but the present invention includes various embodiments. Accordingly, the present invention can be pertinently changed to a software, a hardware or the like.
As an example thereof, in converting grey scale color representing data in a different color representing space to a color representing space in correspondence with a print ink, there may be provided a constitution where a pre conversion color conversion table storing a corresponding relationship of conversion at a small number of lattice points, is used, a color conversion table is formed by increasing the lattice points by interpolation calculation and the color conversion is performed by utilizing the formed color conversion table.
That is, the printer driver refers the color conversion table for converting the grey scale color representing data of the different color representing space in respect of the color representing space in accordance with a print ink and in that case, the lattice points are increased by performing an interpolation from the pre conversion color conversion table at a small number of the lattice points and the color conversion is performed by using the color conversion table where the lattice points are increased.
When an example of implementing the thought of the present invention is constituted by a software of a color conversion device, the example is naturally present on a record medium for recording the software and is utilized. Naturally, the record medium may be a magnetic record medium or may be a photomagnetic record medium and may quite similarly be any record medium to be developed in the future. Further, the same goes with stages of copying a primarily copied product, a secondarily copied product or the like. Additionally, in the case of a software, in the installing operation, the processing of increasing lattice points can be performed and even in the case where a communication network is utilized as supply method, the present invention is invariably utilized. In this case, the side of providing the software by utilizing a communication network, functions as a software providing device and the present invention is similarly utilized.
Further, the thought of the present invention remains unchanged even in the case where the present invention is realized partially by a software and partially by a hardware and the present invention may be of a mode where a portion of the present invention is stored on a record medium and is read pertinently as necessary. Furthermore, the present invention is naturally applicable to a color facsimile device, a color copier, a color scanner, a digital still camera, a digital video camera or the like utilizing such a color conversion table.